chapter 17 electric potential - millerstem

Chapter 17

Electric Potential

17.1 Electrostatic Potential Energy and

Potential Difference

The electrostatic force is

conservative – potential

energy can be defined

Change in electric potential

energy is negative of work

done by electric force:

(17-1)



Electric potential is defined as potential

energy per unit charge:

(17-2a)

Unit of electric potential: the volt (V).

1 V = I J/C.



Only changes in potential can be measured,

allowing free assignment of V = 0.

(17-2b)



Analogy between gravitational and electrical

potential energy:

17.2 Relation between Electric Potential

and Electric Field

Work is charge multiplied by potential:

Work is also force multiplied by

distance:

17.2 Relation between Electric Potential

and Electric Field

Solving for the field,

(17-4b)

If the field is not uniform, it can be

calculated at multiple points:

17.3 Equipotential Lines

An equipotential is a line or

surface over which the

potential is constant.

Electric field lines are

perpendicular to

equipotentials.

The surface of a conductor is

an equipotential.

17.3 Equipotential Lines

17.4 The Electron Volt, a Unit of Energy

One electron volt (eV) is the energy gained by

an electron moving through a potential

difference of one volt.

17.5 Electric Potential Due to Point

Charges

The electric potential due to a point charge

can be derived using calculus.

(17-5)


Charges

These plots show the

potential due to (a)

positive and (b) negative

charge.


Charges

Using potentials instead of fields can make

solving problems much easier – potential is a

scalar quantity, whereas the field is a vector.

17.6 Potential Due to Electric Dipole;

Dipole Moment

The potential due to an electric dipole is

just the sum of the potentials due to each

charge, and can be calculated exactly.

17.7 Capacitance

A capacitor consists of two conductors

that are close but not touching. A

capacitor has the ability to store electric

charge.

17.7 Capacitance

Parallel-plate capacitor connected to battery. (b)

is a circuit diagram.

17.7 Capacitance

When a capacitor is connected to a battery, the

charge on its plates is proportional to the

voltage:

(17-7)

The quantity C is called the capacitance.

Unit of capacitance: the farad (F)

1 F = 1 C/V

17.7 Capacitance

The capacitance does not depend on the

voltage; it is a function of the geometry and

materials of the capacitor.

For a parallel-plate capacitor:

(17-8)

17.9 Storage of Electric Energy

A charged capacitor stores electric energy;

the energy stored is equal to the work done

to charge the capacitor.

(17-10)

17.10 Cathode Ray Tube: TV and

Computer Monitors, Oscilloscope

A cathode ray tube

contains a wire cathode

that, when heated, emits

electrons. A voltage

source causes the

electrons to travel to the

anode.



The electrons can be steered using electric or

magnetic fields.



Televisions and computer monitors (except for

LCD and plasma models) have a large

cathode ray tube

as their display.

Variations in the

field steer the

electrons on their

way to the screen.

chapter 17 electric potential - millerstem

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